Azomethine, carbonyl and thiocarbonyl ylides

Abstract

Abstract Simple addition of a carbene or carbenoid to a C-N double bond would be expected to result in the formation of an azomethine ylide. This is consistent with electrophilic attack of the carbene at the nitrogen atom lone pair. Formation of ylides in this manner was reviewed by Padwa and Hornbuckle in 1991. The reaction of carbenes with simple imines (Schiff bases) to form azomethine ylides, which then undergo 1,3-dipolar cycloaddition with a second molecule of imine, was first reported in 1972. Bartnik and Mloston subsequently extended this method by using various dipolarophiles. Catalytic decomposition of phenyldiazomethane with N-benzylidenemethylamine results in the formation of a trans-1,3-dipole which then undergoes [3+2]-cycloaddition with an available 1r-bond. This is illustrated by the synthesis of 1-methyl-2,5-diphenyl-3,4-dicarboxylic acid dimethyl ester 1 from phenyldiazomethane, N-benzylidenemethylamine and dimethyl maleate (Scheme 3.1.1). This reaction takes place in a highly diastereoselective manner giving only the r-2,t-3,t-4,t-5 isomer (Beilstein’s r,c,t-system).